Degassing of flowable masses in a multiple-screw extruder

ABSTRACT

The invention relates to a multiple-screw extruder that comprises a first process chamber ( 1 ) and a second process chamber ( 2 ). In the degassing zones of said extruder, at least the first process chamber is provided with at least one degassing opening. The radius R of the conveyor element in the degassing zones, in at least one conveyor element ( 7; 9 ) of at least one screw ( 5, 7; 5, 9 ) configured as a passage screw, in a subsection configured as a passage subsection ( 71   a   , 71   e   ; 91   a   , 91   e ), along the peripheral direction of the at least one conveyor element ( 7; 9 ) is by ΔR smaller than the full radius Rv of the conveyor element ( 6; 8 ) required for the mutual stripping of adhering product in a closely intermeshing screw operation with die adjacent conveyor elements ( 6; 8 ) of adjacent conventional screws ( 5, 6; 5, 8 ). The invention also relates to a method for degassing viscous or elasticoviscous flowable masses in such a multi-screw extruder having several process chambers, the respective process chambers communicating by means of a connecting opening.

The present invention relates to a multiple-screw extruder and a methodof degassing viscous or viscoelastic flowable masses in a multiple-screwextruder having multiple process chambers according to the preamble ofclaim 1 and according to claim 18.

For the degassing of viscous masses, such as polyester melts, orviscoelastic masses, such as rubber mixtures, in a multiple-screwextruder, the mass to be degassed is typically distributed within themultiple-screw extruder in multiple process chambers depending on thearrangement of the screws, which are equipped with processing elements.

In known multiple-screw extruders and methods of the type initiallycited, these process chambers are separated from one another in at leastsome sections along the extruder conveyance direction (lengthwisedirection), either by screws having closely intermeshing and mutuallystripping conveyor elements, so that hardly any material exchange(neither gas nor mass) occurs between neighboring process chambers inthese chambers, or they are connected to one another by regions in whichone or more screws has no processing element, so that material exchange(gas and mass) may occur between the process chambers.

For multiple-screw extruders having multiple process chambers, until noweither closely intermeshing or non-closely intermeshing conveyorelements were always used, so that either a stripping, self-cleaningeffect of neighboring screws was achieved, but practically without anymaterial exchange between the process chambers, or a noticeable materialexchange is achieved between the process chambers, but without thestripping, self-cleaning effect of neighboring screws. This isespecially disadvantageous if regions of this type having conveyorelements are located in the region of degassing openings of theextruder.

The present invention is therefore based on the object, in amultiple-screw extruder having multiple process chambers of theconstruction initially cited, of ensuring both a self-cleaning effect ofthe conveyor elements and material exchange between different processchambers, particularly in the region of the degassing zones.

This subject is achieved by the multiple-screw extruder according toclaim 1 and the method according to claim 18.

Further advantageous embodiments of the present invention result fromthe subclaims.

Further advantages, features, and possible applications of the presentinvention result from the following description of two exemplaryembodiments of the present invention with reference to the attacheddrawing, in which:

FIG. 1 is a schematic sectional view perpendicular to the conveyanceand/or lengthwise direction of a ring extruder of the related art.

FIG. 2 is a schematic view of a detail of the arrangement of the screwsin a first exemplary embodiment of the multiple-screw extruder accordingto the present invention, the first process chamber being positionedbelow the plane of the drawing and the second process chamber beingpositioned above the plane of the drawing.

FIG. 3 is a sectional view of the sectional plane III-III of FIG. 2.

FIG. 4 is a schematic view of a detail of the arrangement of the screwsin the second exemplary embodiment of the multiple-screw extruderaccording to the present invention, the first process chamber beingpositioned below the plane of the drawing and the second process chamberbeing positioned above the plane of the drawing.

FIG. 5 is a sectional view of the sectional plane V-V of FIG. 4.

FIG. 1 is a sectional view of a ring extruder of the related art along asectional plane perpendicular to the conveyance and/or lengthwisedirection of the extruder. In this case, the ring extruder includes 12screws 5 positioned parallel to the lengthwise and/or conveyancedirection of the extruder like a collar, each of which carries adouble-threaded conveyor element 6. The 12 screws 5 positioned like acollar are implemented as closely intermeshing, so that the outerprocess chamber 1 of the ring extruder is separated from the innerprocess chamber 2 of the ring extruder. The screws 5 positioned like acollar are mounted between a housing 3 and a core 4, which is fixed inrelation to the housing. The face of the housing 3 which faces towardthe screw collar appears in the cross-sectional view as the outer flower10. The face of the core 4 which faces toward the screw collar appearsin cross-section as an inner flower 11.

FIG. 2 is a schematic view of a detail of the screw arrangement in afirst exemplary embodiment of the multiple-screw extruder according tothe present invention, whose conveyor elements 6, 7 are each implementedas double-threaded conveyor elements. In order to simplify theillustration, the 4 conveyor elements illustrated are shown lying nextone another in one plane (plane of the drawing). In reality, however,they may be positioned both in a plane and like a collar on acylindrical surface, as in a ring extruder, for example. The conveyorelements 6, 7 are double-threaded conveyor elements, double-threadedconveyor elements 6 without clipping and double-threaded conveyorelements 7 with clipping following one another alternately. The clippingin the clipped double-threaded conveyor elements 7 is produced in that,for the first land 71, this land is clipped by an amount ΔR insubsections 71 a, 71 b, 71 c, 71 d and 71 e of the first land 71, sothat in these regions the radius R is reduced by a differential amountΔR in relation to the complete radius Rv. In the present case, theclipped regions 71 a, 71 b, 71 c, 71 d and 71 e of the first land 71 areeach offset by 180° around the circumference of the conveyor element 7,the second land 72 remaining without clipping. During operation of theextruder, this allows both material exchange along the lengthwisedirection A between the two neighboring threads 73 and 74 of theconveyor element 7 and material exchange between the first processchamber 1 (FIG. 3) and the second process chamber 2 (FIG. 3) of theextruder. A material exchange occurs during operation of the extrudervia the passage subsections 71 a, 71 b, 71 c, 71 d and 71 e. In thiscase, both gas and molten mass may change over from the first processchamber 1 into the second process chamber 2.

FIG. 3 is a sectional view of the section plane III-III of FIG. 2, thehousing 3 and the core 4 of the extruder additionally being shown inthis case. The neighboring screws are a passage screw and a typicalscrew in turn, a double-threaded conveyor element 7, in which a land isclipped in a subsection by an amount ΔR in relation to the completeradius Rv, being attached rotationally fixed on the screw rod 5 of thepassage screw, while a typical conveyor element 6 without clipping,i.e., with a continuous complete radius Rv, is attached rotationallyfixed on the typical screw 5.

FIG. 4 is a schematic view of a detail of the screw arrangement in asecond exemplary embodiment of the multiple-screw extruder according tothe present invention. Instead of the double-threaded conveyor elements6, 7 of FIG. 2, in this case triple-threaded conveyor elements 8, 9 areused. In this case as well, passage screws are positioned alternatelywith typical screws. While the screw rods 5 of the typical screws carryconveyor elements 8 without any clipping, the screw rods 5 of thepassage screw carry conveyor elements 9 having partial clipping. Thetriple-threaded conveyor element 5 has a first land 91, a second land92, and a third land 93, between which a first thread 94, a secondthread 95, and a third thread 96 are implemented. In the present case,the first land 91 of the conveyor element 9 is clipped in subsections 91a, 91 b, 91 c, 91 d and 91 e of the first land 91 by an amount ΔR inrelation to the complete radius Rv. In this case as well, the clippedsubsections of the first land 91 are each offset in relation to oneanother by 180° around the circumference of the conveyor element 9. Inthis case as well, material exchange along the lengthwise direction Abetween the thread 94 and the thread 96 of the conveyor element 9 andbetween the first process chamber 1 (below the plane of the drawing) andthe second process chamber 2 (above the plane of the drawing) is allowedby the connection openings 91 a, 91 b, 91 c, 91 d and 91 e.

FIG. 5 is a sectional view of the sectional plane V-V of FIG. 4. FIG. 5essentially corresponds to FIG. 3, the double-threaded conveyor elements6 (without clipping) and 7 (with clipping) merely being replaced bytriple-threaded conveyor elements 8 (without clipping) and 9 (withclipping). All further reference numbers and/or elements of FIG. 5correspond to the same reference numbers and/or elements of FIG. 3.

In order to also allow material exchange between all threads 94, 95 and96 along the lengthwise direction A in the second exemplary embodiment(FIGS. 4 and 5), in addition to the land 91, the land 92 or the land 93must be clipped in at least one subsection.

Depending on the properties of the viscous or viscoelastic mass to beprocessed, the clipped regions 71 a, 71 b, 71 c, 71 d and 71 e of thefirst land 71 of the double-threaded conveyor element 7 may also extendover a larger region around the circumference.

The same also applies for the clipped regions 91 a, 91 b, 91 c, 91 d and91 e of the first land 91 of the triple-threaded conveyor elements 9 ofthe second exemplary embodiment (FIGS. 4 and 5). In this case as well,the clipped regions of the first land 91 may extend over a largerperipheral region of the triple-threaded conveyor element 9. In theextreme case, the first land 91 of the triple-threaded conveyor element9 may also be completely removed, for example.

Both for the first and the second exemplary embodiment, havingdouble-threaded and triple-threaded conveyor elements, respectively, itis not absolutely necessary for the particular clipped conveyor elements7 and 9 to alternate with unclipped conveyor elements 6 and 8,respectively. Thus, for example, all of the conveyor elements may bepartially clipped or only every third or even every fourth conveyorelement of the neighboring screws may be clipped, etc.

In the figures, the differential radius ΔR and/or the radius R of theconveyor element may be described formally as a function R (φ, x) of theperipheral angle φ around the circumference of the conveyor element andof the axial location x along the axial lengthwise direction of theconveyor element.

List of Reference Numbers

-   1 outer process chamber-   2 inner process chamber-   3 housing-   4 core-   5 screw rod-   6 double-threaded conveyor element without clipping-   7 double-threaded conveyor element with clipping-   8 triple-threaded conveyor element without clipping-   9 triple-threaded conveyor element with clipping-   10 outer flower-   11 inner flower-   71 first land-   72 second land-   73 first thread-   74 second thread-   71 a clipped subsection of the first land/passage subsection-   71 b clipped subsection of the first land/passage subsection-   71 c clipped subsection of the first land/passage subsection-   71 d clipped subsection of the first land/passage subsection-   71 e clipped subsection of the first land/passage subsection-   91 first land-   92 second land-   93 third land-   94 first thread-   95 second thread-   96 third thread-   91 a clipped subsection of the first land/passage subsection-   91 b clipped subsection of the first land/passage subsection-   91 c clipped subsection of the first land/passage subsection-   91 d clipped subsection of the first land/passage subsection-   91 e clipped subsection of the first land/passage subsection-   A lengthwise axis of the screws/conveyance and/or lengthwise    direction

1. A multiple-screw extruder, particularly a ring extruder, havingmultiple screws positioned parallel to one another, in particular like acollar, having processing elements which are implemented along the axialconveyance direction of the extruder in at least some sections asclosely intermeshing, at least double-threaded conveyor elements havingone land per thread, the process chamber of the extruder beingsubdivided in these sections into a first process chamber (1) and asecond process chamber (2) by the screws having the closely intermeshingconveyor elements, and at least the first process chamber being providedwith at least one degassing opening in the degassing zones,characterized in that for at least one conveyor element (7; 9) of atleast one screw (5, 7; 5, 9), which is implemented as a passage screw,in a region around the circumference of the at least one conveyorelement (7; 9) which is implemented as a passage region (71 a, . . . ,71 e; 91 a, . . . , 91 e), the radius R of the conveyor element issmaller by ΔR than the complete radius Rv of the conveyor element (6;8), which is necessary for mutual stripping of adhering product duringclosely intermeshing operation with the neighboring conveyor elements(6; 8) of neighboring typical screws (5, 6; 5, 8).
 2. The multiple-screwextruder according to claim 1, characterized in that the radius R of theconveyor element is smaller than the complete radius Rv by ΔR in thedegassing zones of the extruder.
 3. The multiple-screw extruderaccording to claim 1 or 2, characterized in that the region around thecircumference of the at least one conveyor element (7; 9) which isimplemented as a passage region (71 a, . . . , 71 e; 91 a, . . . , 91 e)is a subsection around the circumference of this conveyor element. 4.The multiple-screw extruder according to one of the preceding claims,characterized in that the differential radius ΔR of the conveyor elementis a function of the peripheral angle φ around the circumference of theconveyor element and a function of the axial location x along the axiallengthwise direction of the conveyor element.
 5. The multiple-screwextruder according to claim 4, characterized in that the differentialradius ΔR of the conveyor element is a symmetrical function of theperipheral angle φ over a complete circumference (0<φ<360°) of theconveyor element.
 6. The multiple-screw extruder according to one ofclaims 3 to 5, characterized in that the subsection is the surface of atleast one land of the lands (71, 72; 91, 92, 93) of the conveyorelement.
 7. The multiple-screw extruder according to one of claims 3 to6, characterized in that the subsection is the surface of at least oneside of the sides of the conveyor element.
 8. The multiple-screwextruder according to one of claims 3 to 7, characterized in that thesubsection is the surface of at least one core region of the coreregions of the conveyor element.
 9. The multiple-screw extruderaccording to one of the preceding claims, characterized in that themultiple screws, which are parallel to one another, are alternatelypassage screws (5, 7; 5, 9) and typical screws (5, 6; 5, 8).
 10. Themultiple-screw extruder according to one of the preceding claims,characterized in that the subsection of the conveyor element of apassage screw (5, 7; 5, 9) which has a radius R smaller than thecomplete radius Rv is a land (71; 91) of the conveyor element (7; 9).11. The multiple-screw extruder according to one of the precedingclaims, characterized in that the subsections of the conveyor elements(6; 8) of a typical screw (5, 6; 5, 8) which may not be stripped usingthe passage subsections (71 a, 71 e; 91 a, . . . , 91 e) of a conveyorelement (7; 9) of a passage screw (5, 7; 5, 9) may be stripped by othercomplete radius circumference subsections of the same conveyor elementof the passage screw.
 12. The multiple-screw extruder according to oneof the preceding claims, characterized in that the multiple-screwextruder is a ring extruder having parallel screws (5) positioned like acollar, particularly circularly, the first process chamber being theouter chamber (1) and the second process chamber being the inner chamber(2) of the ring extruder process chamber (1, 2).
 13. The multiple-screwextruder according to one of the preceding claims, characterized in thatthe conveyor element (7; 9) having the passage subsection (71 a, . . . ,71 e; 91 a, . . . , 91 e) is an n-threaded conveyor element (7; 9), inwhich the radius of at most n-1 lands is a smaller radius than thecomplete radius Rv and the radius of at least one land is the completeradius Rv.
 14. The multiple-screw extruder according to claim 13,characterized in that the conveyor element (7; 9) having the passagesubsection (71 a, . . . , 71 e; 91 a, . . . , 91 e) is a double-threadedconveyor element, in which the radius of the first land is a smallerradius than the complete radius Rv and the radius of the second land isthe complete radius Rv.
 15. The multiple-screw extruder according toclaim 14, characterized in that sequential passage screws (5, 7; 5, 9),which are positioned on both sides of a typical screw (5, 6; 5, 8)positioned between them, are laid out in such a way that as they rotatearound their lengthwise axis A, the particular passage subsection (71 a,. . . , 71 e; 91 a, . . . , 91 e) of a conveyor element is angularlyoffset around the circumference by approximately 180° to thecorresponding passage subsection (71 a, . . . , 71 e; 91 a, . . . , 91e) of the following passage screw.
 16. The multiple-screw extruderaccording to one of the preceding claims, characterized in that nopassage conveyor elements (7; 9), i.e., only closely intermeshingconveyor elements (6; 8), are positioned in a degassing zone, at leastin the region of the degassing opening of the extruder housing.
 17. Themultiple-screw extruder according to one of the preceding claims,characterized in that the passage conveyor element (7; 9) having thepassage subsection (71 a, . . . , 71 e; 91 a, . . . , 91 e) isimplemented around its circumference in such a way that viscous orviscoelastic mass adhering to the passage conveyor element (7; 9) may bestretched by the rotating passage conveyor element into a thin film in acyclic way.
 18. A method of degassing viscous or viscoelastic flowmasses in a multiple-screw extruder having multiple process chambers,which are each separated from one another by multiple screws, positionedparallel to one another, having essentially closely intermeshingconveyor elements, at least one of the process chambers having at leastone degassing zone having a degassing opening and each of the processchambers being partially filled with the mass to be degassed, which isprocessed in each process chamber and conveyed through these processchambers using the conveyor elements of the screws delimiting theparticular process chamber, characterized in that there is at least oneconnection opening between the particular process chambers.
 19. Themethod according to claim 18, characterized in that the multiple-screwextruder has a first process chamber and a second process chamber, whichis separated from the first process chamber by multiple screwspositioned parallel to one another having essentially closelyintermeshing conveyor elements.
 20. The method according to claim 18 or19, characterized in that the connection opening continuously changesduring the operation of the multiple-screw extruder.
 21. The methodaccording to claim 20, characterized in that the change of theconnection opening is that the connection opening moves back and forthcyclically in the region of the degassing zone along the lengthwisedirection A.
 22. The method according to claim 20 or 21, characterizedin that the change of the connection opening is that the extent of theconnection opening cyclically increases and reduces.
 23. The methodaccording to one of claims 18 to 22, characterized in that viscous orviscoelastic mass adhering to the passage conveyor element is so greatlyand rapidly opened cyclically by the rotating conveyor element, havingits cyclically and/or periodically expanding and reducing connectionopening, that the gap is only partially filled with product.
 24. Themethod according to claim 22 or 23, characterized in that the cyclicand/or periodic enlargement and reduction of the connection openingoccurs in such a way that the mass in the region of the connectionopening is stretched into a thin film and pulled over at least asubsection of the connection opening and subsequently destroyed.
 25. Themethod according to one of claims 22 to 24, characterized in that thecyclic and/or periodic enlargement and reduction of the connectionopening occurs in such a way that the mass in the region of theconnection opening changes over from one process chamber into the otherprocess chamber, the surface, of the material being cyclically enlargedand reduced.
 26. The method according to claim 24 or 25, characterizedin that the destruction of the thin film occurs through film rupture dueto the sufficiently rapid stretching of the film.
 27. The methodaccording to one of claims 24, 25 or 26, characterized in that thedestruction of the thin film occurs through film rupture due to thepressure differential between the process chambers on both sides of theconnection opening.
 28. The method according to one of claims 18 to 27,characterized in that the connection opening is a slot-like opening andthe cyclic enlargement and/or reduction of the connection opening isgenerated in that the diametrically opposite longer edge regions of theslot are cyclically moved away from one another and/or toward oneanother.
 29. The method according to one of claims 18 to 28,characterized in that it is performed on a multiple-screw extruderaccording to one of claims 1 to 12, the cyclic movement of the edgeregions of the at least one connection opening toward and away from oneanother being produced through the rotation of the at least one conveyorelement (7; 9) having its passage subsection (71 a, . . . , 71 e; 91 a,. . . , 91 e).